In the current mobile communication environment, second generation (2G), 3G, and 4G long term evolution (LTE) have been commercialized, and introduction of the next-generation 5G system has been considered. In accordance with communication systems, communication service providers, and nations, various mobile communication service frequency bands coexist, and base station environments have also been diversified. Accordingly, in order to implement an efficient base station system and to save the base station operation cost, broadband and multi-band systems that can cover various service bands have been constructed in a base station (and base station antenna).
FIG. 1 is a schematic block diagram illustrating an example of the configuration of a general multi-band mobile communication base station antenna. Referring to FIG. 1, a multi-band mobile communication base station antenna 10 has a multi-band antenna structure capable of servicing a first frequency band Band1 and a second frequency band Band2. The first frequency band may be, for example, a US-personal communication service (US-PCS) band of 1.9 GHz (e.g., 1.850 to 1.995 GHz), and the second frequency band may be, for example, a broadband radio service (BRS) band of 2.5 GHz (e.g., 2.495 to 2.690 GHz).
In the base station antenna 10, although separate radiation elements for respective frequency bands may be provided, for miniaturization of the corresponding base station antenna 10, a plurality of radiation elements of common first and second frequency bands, for example, first to fifth radiation elements 111, 112, 113, 114, and 115, may be configured to be vertically arranged in a line. The first to fifth radiation elements 111 to 115 are broadband radiation elements having the broadband characteristics, and are provided to cover a band having about 45% fractional bandwidth. The radiation elements may have, for example, the operation characteristic of 1710 to 2690 MHz.
In such a structure, in order to provide an electrically vertical tilt with respect to the overall radiated beams of the first frequency band, an input signal In1 of the first frequency band is dividedly output to the first to fifth radiation elements 111 to 115, and phases of respective divided signals through the first to fifth radiation elements 111 to 115 are shifted by a first multi-line phase shifter 121 so that the divided signals have predetermined phase differences between them. In the same manner, in order to provide an electrically vertical tilt with respect to the overall radiated beams of the second frequency band, an input signal In2 of the second frequency band is dividedly output to the first to fifth radiation elements 111 to 115, and phases of respective divided signals through the first to fifth radiation elements 111 to 115 are shifted by a second multi-line phase shifter 122 so that the divided signals have predetermined phase differences between them. An example of such first and second multi-line phase shifters 121 and 122 is disclosed in the applicant's prior application, Korean Patent Application No. 2009-40978 (title: Multi-line phase shifter for vertical beam tilt control antenna, application date: May 11, 2009, Inventors: Young-chan Moon, O-suk Choi, In-ho Kim, and kwang-suk Choi).
On the other hand, the plurality of divided signals through the first to fifth radiation elements 111 to 115 of the first multi-line phase shifter 121 and the plurality of divided signals through the first to fifth radiation elements 111 to 115 of the second multi-line phase shifter 122 are correspondingly combined through first to fifth frequency combiners/dividers 131, 132, 133, 134, and 135 to be provided to the corresponding radiation elements. In this case, transferring of the plurality of signals between the first and second multi-line phase shifters 121 and 122 and the first to fifth frequency combiners/dividers 131 to 135 is performed through a feeding cable of a predetermined standard, such as a coaxial cable. Each of the first to fifth frequency combiners/dividers 131 to 135 may have a diplexer or duplexer structure in which a filter portion for filtering the first frequency band and a filter portion for filtering the second frequency band are combined.
As illustrated in FIG. 1, in a multi-band base station antenna, the respective bands have different electrical beam tilting conditions, and separate multi-line phase shifters are required to perform beam tilting for the respective bands. In this case, since a relatively large number of feeding cables should be installed for connection between the respective multi-line phase shifters and the plurality of frequency combiners/dividers, the multi-band base station antenna has the problem that the internal structure of the multi-band base station antenna becomes complicated or the overall size is increased.
In order to solve this problem, various schemes for optimizing the installation locations or connection structures of the plurality of multi-line phase shifters and the plurality of frequency combiners/dividers in the multi-band base station antenna have been considered, but their effects are relatively insignificant.